In recent years, elastic wave elements have been used in a duplexer that filters signals transmitted from or received by an antenna in a communication device such as a mobile terminal. An elastic wave element is formed of a piezoelectric substrate and an excitation electrode on a main surface of the piezoelectric substrate. The elastic wave element utilizes a characteristic that an electric signal and a surface acoustic wave can be converted to each other in accordance with a relationship between the excitation electrode and the piezoelectric substrate.
A duplexer includes a plurality of elastic wave elements and thereby serves as, for example, a reception filter and a transmission filter (see, for example, Japanese Unexamined Patent Application Publication No. 2007-214902). With a plurality of elastic wave elements being combined, passbands of reception and transmission bands are set in the duplexer.